The present application is based on and claims priority to JP 2001-052209 filed in the Japanese patent office on Feb. 27, 2001, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to a solid state laser apparatus.
2. Discussion of the Background
A solid state laser apparatus irradiates light or a beam of a lamp or semiconductor laser (e.g., laser diode, which is hereafter referred to by xe2x80x9cLDxe2x80x9d), as an excitation source, to a solid excitation medium, such as a YAG rod, to excite the YAG rod for emission of a laser beam. An example of such a solid state laser apparatus is shown in FIG. 1, which apparatus includes a cavity 1. A YAG rod 2 is concentrically inserted in a glass, or the like, transparent flow tube 3 in the cavity 1. An excitation lamp 4 is used as the excitation source located in the cavity 1 outside of the flow tube 3 so as to laterally sandwich the YAG rod 2. A rod holder 5 holds a corresponding axial end of the YAG rod 2 (only one side of the apparatus is shown in FIG. 1). A light duct 6 is placed outwardly of the rod holder 5 in an axial direction of the YAG rod 2 to extrude from the cavity 1. Thus, the YAG rod 2, rod holder 5, and light duct 6 are axially aligned with one another.
The solid stage laser apparatus further includes a cooling water channel 7 in the flow tube 3 for cooling the YAG rod 2, a cooling water channel 8 in the cavity 1 for cooling the excitation lamp 4, a block 9 in the cavity 1 for holding an end of the excitation lamp 4, and an O-ring 10 for sealing between the light duct 6 and cavity 1.
Particulars of the rod holder 5 are shown in section in FIG. 2 in an enlarged scale. The rod holder 5 is a hollow cylinder with opposite open ends, one of which is an opening 5a adjacent to the YAG rod 2 and with an inner diameter substantially equal to an outer diameter of the rod 2. The end of the YAG rod 2 is fitted into the opening 5a. 
Concentrically fitted into the rod holder 5 is a hollow inner cylinder 11 with opposite open ends and having an inner diameter larger than the outer diameter of the YAG rod 2. The inner cylinder 11 has, at its end adjacent to the YAG rod 2, a flange 11a with an opening whose diameter is substantially equal to the outer diameter of the YAG rod 2. An end face of the flange 11a adjacent to the YAG rod 2 is perpendicular to the axis of the inner cylinder 11. Fitted into a space surrounded by the end face of the flange 11a and a tapered portion 5b of the rod holder 5 is an O-ring 12 which is fitted over an outer periphery of an end of the YAG rod 2 to prevent the cooling water in the channel 7 from leaking into the inner cylinder 11.
Screwed into a thread on an inner surface of the rod holder 5 midway in its longitudinal direction is a pressure ring 13 which has an inner diameter substantially equal to that of the inner cylinder 11. Thus, axial adjustment in a position of the pressure ring 13 allows the O-ring 12 to be pressed with a predetermined pressure axially of the YAG rod 2 via the flange 11a of the inner cylinder 11. Thus, the O-ring 12 is expanded radially of the YAG rod 2 so that the YAG rod 2 is held in a predetermined state radially of the rod holder 5 by a grasping force generated from the expansion of the O-ring 12.
Fitted into the end of rod holder 5 away from the YAG rod 2 is an end of the light duct 6 which has portions respectively with inner diameters substantially equal to and larger than that of the inner cylinder 11. Mounted on an outer periphery of the fitted portion of the light duct 6 to the rod holder 5 is an O-ring 15 which prevents the cooling water in the channels 7 and 8 from leaking into, for example, the hollow spaces of the inner cylinder 11 and light duct 6.
In the above solid state laser apparatus, light is irradiated by the excitation lamp 4 to the YAG rod 2 to generate a laser beam which is output through the hollow spaces in the inner cylinder 11, pressure ring 13, and light duct 6 to the outside of the apparatus. The output laser beam is amplified through its resonation between laser mirrors (not shown) which are installed on axially opposite sides of the YAG rod 2 to sandwich the cavity 1.
To obtain a greater laser output, the above-mentioned solid state laser apparatus must be arranged in a multistage with plural YAG rods 2 aligned with one another. However, in the above-mentioned structure with each YAG rod 2 held by the O-ring 12 made of rubber, it is next to impossible to uniformly pressurize a periphery of a grasped portion of the YAG rod 2, which thereby results in failing to control an eccentricity of the YAG rod 2. Moreover, a centering accuracy of the YAG rod 2 is inherently hard to obtain since manufacturing tolerance of the O-ring 12 is too great in comparison with the required centering accuracy of the YAG rod 2.
Also, irradiation of the light of lamp or LD from the excitation lamp 4 or the returned laser beam to the O-ring 12 may cause the O-ring 12 to deform because of degassing. Moreover, depending upon the material, the O-ring 12 may be hydrolyzed by the cooling water, though it may be resistant to heat. Aging due to such degassing or hydrolysis may also cause the O-ring 12 to deform, resulting in increased eccentricity of the YAG rod 2. The degassing or hydrolysis may also significantly degrade cleanliness of the opposite ends of YAG rod 2, which cleanliness is significant for proper output of the laser beam, resulting in instability and unreliability of the output of the solid state laser apparatus.
In addition, the inner cylinder 11 and pressure ring 13 are required as components which press the O-ring 12 axially of the apparatus to ensure expansion of the O-ring 12 in its radial direction, which leads to structural complication of the components of the apparatus.
In view of the above, the present invention has as one object to provide a novel solid state laser apparatus that is structurally simple in components but that enables accurate centering of a YAG rod.
A further object of the present invention is to provide a novel solid state laser apparatus which causes neither degassing nor hydrolysis, to thereby improve stability and reliability of the output.
In order to achieve the above object, and overcome the above-mentioned problems in the background art, in one embodiment a solid state laser apparatus according to the invention includes a cavity having a longitudinal hollow with opposite open ends. A cylindrical solid state excitation medium is accommodated in the hollow of the cavity. A solid-state-excitation-medium holder in the form of a hollow cylinder is inserted into each of the opposite open ends of the hollow and is fitted over a corresponding end of the excitation medium. A seal is fitted into a hollow of the holder adjacent to a portion of the holder fitted over the end of the excitation medium. The seal can include an annular seal body with a U-shaped section, made from a resin free of degassing and hydrolysis and fitted over an outer periphery of the end of the excitation medium to grip the excitation medium, as well as a spring fitted into a groove of the seal body provided by the U-shaped section so as to circumferentially surround a gripped portion of the excitation medium. Preferably, the seal body is made from Teflon(copyright).
In the invention, the cylindrical solid state excitation medium can be accurately centered since the gripped portion of the excitation medium is uniformly and circumferentially pressurized through the seal body by the spring. Furthermore, eccentricity of the excitation medium and contamination of the end faces of the same due to aging of the seal body can be prevented since degassing or hydrolysis does not occur in the seal body; as a result, stability and reliability of the output of the apparatus can be improved. Also, the apparatus is structurally simple in components and compact in size since no mechanism is required for pressing the seal axially of the apparatus.